X9241A
Detailed Operation
All four XDCP potentiometers share the serial interface and
share a common architecture. Each potentiometer is
comprised of a resistor array, a Wiper Counter Register and
four Data Registers. A detailed discussion of the register
organization and array operation follows.
The WCR is a volatile register; that is, its contents are lost
when the X9241A is powered-down. Although the register is
automatically loaded with the value in DR0 upon power-up, it
should be noted this may be different from the value present
at power-down.
Data Registers
Each potentiometer has four nonvolatile Data Registers.
These can be read or written directly by the host and data
can be transferred between any of the four Data Registers
and the WCR. It should be noted all operations changing
data in one of these registers is a nonvolatile operation and
will take a maximum of 10ms.
If the application does not require storage of multiple
settings for the potentiometer, these registers can be used
as regular memory locations that could possibly store
system parameters or user preference data.
Wiper Counter Register
The X9241A contains four volatile Wiper Counter Registers
(WCR), one for each XDCP potentiometer. The WCR can be
envisioned as a 6-bit parallel and serial load counter with its
outputs decoded to select one of sixty-four switches along its
resistor array. The contents of the WCR can be altered in
four ways: it may be written directly by the host via the Write
WCR instruction (serial load); it may be written indirectly by
transferring the contents of one of four associated Data
Registers via the XFR Data Register instruction (parallel
load); it can be modified one step at a time by the
increment/decrement instruction; finally, it is loaded with the
contents of its Data Register zero (DR0) upon power-up.
Serial Data Path
From Interface
Circuitry
Register 0
8
Register 1
6
Serial
Bus
Input
V
H
/R
H
Parallel
Bus
Input
Wiper
Counter
Register
Register 2
Register 3
C
o
u
n
t
e
r
2
If WCR = 00[H] then V
W
/R
W
= V
L
/R
L
If WCR = 3F[H] then V
W
/R
W
= V
H
/R
H
UP/DN
Modified SCL
INC/DEC
Logic
UP/DN
CLK
DW
Cascade
Control
Logic
CM
D
e
c
o
d
e
V
L
/R
L
V
W
/R
W
FIGURE 8. DETAILED POTENTIOMETER BLOCK DIAGRAM
8
FN8164.5
December 14, 2006
INTERSIL [ INTERSIL CORPORATION ]
